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S. B. WILLIAMS,JR., AND BEG. DUNHAM.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED mzc.27.191s.

1,355, 34, Patented 00t.12,1920.

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S. B. WILLIAMS, JII., AND B. G. DUNHAM.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED DEC.27.1918.

1 55,634. Patented Oct. 12, 1920.

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SAMUEL IB. WILLIAIvIS, JR, OF BROOKLYN, NEW YORK, AND BERT G. DUNHAM, OF

HAWTHORNE, NEW JERSEY, ASSEGNCIRS T9 WESTERN ELECTRIC COMPANY, IN- CORPORATED, OF NEW YORK, N. "25., A CORPORATIGN OF NEW YORK.

' TELEPHOIilE-EZSICHANGE SYSTEM.

Specification of Letters Patent.

Application filed December 27, 1818. Serial No. 268,468.

To aZZ whom it may concern Be it known that we, SAMUEL B. W n- Passaic, State of New Jersey, respectively,

have invented. certain new and useful Tmprovements in Telephone-Exchange Systerns. or which-the following is a full, clear, concise, and exact description.

This invention relates to an improvement in telephone exchange systems and has particular reference to a semi-mechanical private branch exchange system employing rotary line and selector switches.

The present invention is designed as a means for establishing various connections through a'trunking arrangement shown in an application to S. B. Williams, J12, filed on December 27, 1918, andbearin Serial No. 268,501, and wherein groups or trunks in a selector switch are provided, certain or" which have their terminals interspersed in the terminal bank, while other terminals in the bank are allotted for group selection.

An object of the invention is to provide a selector switch in which means are employed, whereby an idle trunk in any group individual to one of said means may be se lected, without the possibility of seizing an idle trunk in any other group over which the brushes of the switch may move.

Another object is the provision of a final selector or connector switch, wherein selection of certain. groups of final trunks and trunks in said groups is made in accordance with impulses transmitted to said switch, and wherein the selection of another group on: trunks occurs between the sending or different sets of impulses.

The inventive idea involved is capable of receiving a variety of expressions, one of which, for the purpose of illustrating the invention, is shown in the accompanying drawings, but it is to be expressly understood that said drawings are employed merely for the purpose o1 illustrating the invention as a whole and not to define the limits thereo't', reference being had to the appended claims for this purpose.

In the drawings Figures 1 and 2 combined, with Fig. 2 at the right of Fig.1,

illustrate diagrammatically the various cir cuits of the private branch exchange system; Fig. 3 is a diagrammatic View of the trunkmg arrangement employed in connection with the invention.

In carrying out the invention, switches ot the rotary type having contacts arranged in Patented Oct. 12, 1920.;

a complete circle are preferably employed 7 for interconnecting the telephone lines. In Fig. 3 wherein the trunking arrangement is disclosed, a subscribers' substation A is shown in association with a line switch B, the brushes of which are caused to move over theterrninal bank by the removal of the receiver at substation A and automatically select an idle trunk, whereby the line is extended to a first selector switch C. The multiple bank or" this switch consists of a plurality oi terminals, certain of which are available for trunks divided into groups. Two of these groups 0 and 0' are available for automatically extending a connection to selector switches D when interconnecting calling and called subscribers within the private branch exchange. The terminals of aid groups in the multiple bank of switch 0 are shown as arranged alternately, but it is to be understood that said terminals may be promiscuously interspersed or disposed at random without departing from the spirit and scope of the invenion. The multiple of the several banks is such that a different trunk appears as the first trunk in each multiple bank or group of multiple banks. By this arrangement, the selectors will not be required to hunt over all the busy trunks and the number of busy trunks passed over will be on the average, the same when calling through the. first group as when calling through the second group. The other two groups of trunks 0 and 0 may be used in establishing connections to a private branch exchange operatofsposition and to a cen tral oliice exchange, respectively, and the terminals in the trunks of each of these groups, in contradistinction to the terminals of groups of trunks c and 0 are preferably arranged in the ordinary manner.

In the final selector switch 1), three groups of lines (5, (Z and (Z are shown, and depending upon the number of tens impulses transmitted by the sender at substation A. in making an automatic connection to a called substation, the brushes of the final selector are stepped around to one of three terminals. The units digits of numbers in the first two groups are selected by the dial impulses, but when a number in the last group is called, a group relay operates on the completion of the impulses for the tens digit, as will appear later, causing'the stepping magnet of the final selector to automatically step the brushes around to the last group, and the dialing of the units 7 it of the number then selects the desired trunk in this group.

The operation may be briefly stated as follows: Should a subscriber at substation A desire a connection to the central oliice exchange, the removal of his receiver will first operate line switch B to seize an idle trunk. The impulse sender is then manipulated to transmit one impulse which will step the brushes of the first selector switch C to the second terminal of the multiple bank, and thus select the group of central ofiice trunks 0 By this selection the terminals of all the other groups of trunks are rendered nonselectable, and the brushes of the switch will he stepped over these terminals and caused to hunt for an idle trunk in the group 0 whereupon the connection will be extended to the central oflice.

If it is desired to automatically establish a connection between two subscribers within the private branch exchange, the calling sub scriber will, by removing his receiver, seize an idle trunk connected to the line switch, and by manipulating the sender to trans mit two or three impulses, depending upon which of the groups 0 or 0 is to be selected, the brushes of the selector C will he stepped to the corresponding terminal in the selector bank allotted to the particular group, whereupon a trunk hunting operation will proceed over the terminals of the group of trunks selected.

As previously stated in connection with the trunk hunting in group 0*, the terminals of all the other groups, with the exception of the one in which trunk hunting is now proceeding, will likewise be made non-selectable, so that should all the trunks in the selected group be busy, the brushes of the selector will travel over the groups of trunks c and 0 in order that a busy tone will be transmitted to a subscriber at substation A. Upon the seizing of a trunk in either of the two groups 0 or 0 the line is extended tothe final selector switch which is operated, as briefly referred to above, to connect the calling and called subscribers.

To call the private branch exchange operator, the digit 0 is dialed to send ten impulses after a connection has been extended from the line switch, and the brushes of the selector are stepped to the terminal of the bank in association with the group of trunks 0 at which-time a trunk hunting operation would again take place to select an idle trunk leading to the operators position. Again, as described in connection with the trunlrhunting operations in other groups, the terminals thereof, in this instance, will be rendered non-selectable in order that trunks therein will not be seized.

It is believed that the invention will now be best understood froma detailed description of the operation in establishing a connection from calling subscriber to a called subscriber, and also to central on' ice and private branch exchange trunks. Ilpon the removal of the receiver at substation A, in initiating a call, line relay 200 of the line switch 13 is energized over a circuit from grounded battery, winding of relay 200, back contact and innermost lower armature of cutoff relav' 201 substation apparatus.

. i li upper armature and back contact of relay 201 to ground. The marginal stepping magnet 202 is then energized over the circuit from grounded battery, winding of said magnet, armature and baclr contact thereof, front contact and armature of line relay 200 and lowermost brush 203to ground at the normal terminal thereof, whereupon the brushes of the switch will be stepped to the second set of terminals, the trunks of which lead to one of the first selector switches. Should the selector switch connected to the first test terminal be busy, brush 203 of the line switch B engaging said terminal will be grounded at the back contact of the line relay of the line switch connected to said lector switch, and a circuit will be found for stepping magnet 202 extending from grounded battery, winding of said magnet, armature and back contact thereof, front contact and armature of relay 200, brush 203, armature and back contact of the line relay of said other line switch to ground. Magnet 202 being self-interrupting, will again step the brushes of the line switch over the terminal bank until an idle trunk is found, whereupon a circuit is established from grounded battery, winding of magnet 202, back con tact and armature thereof, winding of relay 201 in series with said magnet, brush 204, conductor 304, winding of low resistance relay 307, brush 308 of the selector switch, bacl: contact and innermost right armature of test relay 303, and right armature of relay 301 to ground. Magnet 202. being marginal and in series with relay 201, will not operate, but relays 201 and 307 will operate and the former relay will extend the subscribers line to the idle selector switch C. Line relay 200 deenergizes and its back contact grounds the test terminal and makes the trunk test busy to all other line switches.

Line relay of the selector switch will re imcler ely upon energization of 307 due t0 the circuit extending from .grounded battery, right winding of relay 309, armature and front contact of relay 307 to ground. A circuit for relay 309 will be 310, left winding of relay 309, brush 311 and coil 312 to ground. First slow-to-release relay 305 is then energized by a circuit extending from grounded battery, winding of re lay 305 and'front contact and armature'of line relay 309 to ground. Operation of rela 305 establishes a holding circuit for'relay 201 extending from grounded battery, winding'of magnet 202, armature and contact thereof, winding of relay 201, brush 20a, conductor 30 1, and left armatur of relay 305 to ground. A. tone is furnished by coil 312 to-inform the subscriber that he may now operate his sending device. If the subscriber desires to establish a connection to another P. B. X. subscriber, he will now transmit two or three impulses, depending upon which group of trunks 0 or 0 is to be selected for the trunk hunting operation. Interruption of the circuit of line relay 309 by the sending device, causes the armature thereof to vibrate, and upon each retraction a circuit is closed for the stepping magnet 313, extending from grounded battery, winding of magnet 313, windingof slow-torelease relay 301, right armature of slow-torelease relay which remains energized during the line interruptions, back contact and outermost lower armature of cutoil re lay 310 and back contact of the armature of relay 309 to ground. The brushes of the selector are stepped from their normal terminals in accordance with the number of im pulses sent, and upon dehnergization of relay 301 at thetermination of the transmission of impulses, one of the two group re lays 3141- and 315 is energized. Assuming that two impulses were sent to select the group of trunks 0'', group relay 31. 1- will be energized ov a circuit extending from grounded battery, winding of relay 31%, brush 303 which now rests upon the third terminal in its row, back contact and innermost right-hand armature of test relay 303, and right armature of relay 301 to grounljl. Relay 314iin attracting its right armature,

energizes test relay 303, orer a circuit ere third terminal in. the row associated with arinatu re said brush, front contact and right relay 303 of rel y 314 to ground. After test is energized, relay i idle trunk is for and left armature of slow-to-release relay 305 to ground. Steppingmagnet 313 is'nowoperated over a circuit extending from Ollntl( lfl battery, winding of said magnet, mature and back contact thereof, front Contact and outer left armature of relay 303, front contact and right armature of relay 314C to ground. It is to be noted that the continued energization of relay 314 has removed the ground at its right armature from the terminals of the selected group 0 traversed by the brush 316, but that as long as the test brush 317 of'the selector is moving over busy trunks, test relay 303 is held up over a circuit from grounded battery, left winding of relay 303, front contact and inner left armature thereof, test brush 317 to ground at the busy final selector. it is therefore apparent that relay 303 will not r lease until brushes 316 and 317 engage two terminals simultaneously free from ground and consequently stepping magnet 313 continues to operate until an idle trunk is found. During the energization of test relay 303, a ground is placed upon the conductor 302, except when relay 301 is energized, and this ground provides an addiional guarding potential which will prevent seizure of the selector by another line switch when the latter is hunting for anidle trunk. When brushes 316 and 317 simultaneously two terminals free from ground, test relay 303 will retract its armatures an break the circuit for stepping magnet 313, and brushes of the selector will come to rest upon the selected terminals. Cutoff relay 310 is immediately energized bythe circuit extending from grounded battery, winding relay 310, back contact and outer rignt armature of test relay 303,, brush 303, back contact and inner right armature of test relay 303 and back contact and armature of relay 301 to ground, and the line is thus e:-:-' tended to the final selector switch D. Upon the operation of cutohf relay 310, line relay 309 and slou -to-release relay 305 release,but the upper and inner lower armatures of relay 310 being of the maizebefore-break type, the connection is cut through and ground is found at the final selector for relay 201 and group relay 314, before the ground at relay 305 is removed, and said relays thus remain energized.

If all of the trunks in the group are found to be busy, test relay 303 remains energized until the brushes of the switch have been stepped onto the last set of terminals, at which time brush 317, no longer finding ground, will cause relay 303 to deenergize, and upon the release of relay 303, cutoff relay 310 is energized over a circuit extend ing from grounded battery, winding of relay 310, back contact andouter right armature of relay 303, brush 317, inner left-hand armature and back contact of .relay 303,

side of the telephone line, substation apparatus A, upper side of the telephone line, brush 319 and coil 325 to ground. Through this circuit relay 300 is held energized until the receiver at substation A is replaced upon its hook. Line relay 309. then releases whereupon the slow-to-release relay 305 will become deenergized. This latter relay opens a circuit for the relay 310 at its left-hand front contact above described. The release of relay 310 closes a circuit from ground,

the armature and back contact of relay 309, the lower armature and back contact of relay 310, right-hand armature and back con tact of relay 305, brush 316, and right-hand winding of relay 303 to grounded battery. The energization of relay 303 closes a circuit for stepping magnet 313 from grounded battery, the winding, armature and back contact of said magnet, left-hand outer front contact and armature of relay 303, left-hand back contact and armature of relay 305 to ground, whereupon stepping magnet 313 will become energized and step the switch to normal position at which position relay 303 will be deenergized and the circuit is then restored to its normal condition. The line switch is restored to normal in a manner to appear later.

Assuming now that an idle trunk was found, upon the energization of cutoff relay 310. line relay 400 of the final selector switch D becomes energized over the circuit extended from grounded battery, right winding of relay 400, lower side of the telephone line, substation apparatus A, upper side of the telephone line and left winding of relay 400 to ground. In attracting its armature,

relay 400 closes the circuit for slow-to-release relay 401 which extends from grounded battery, winding of relay 401, front contact and armature of relay 400 to ground. Relay 401 attracts its left armature and establishes the ground previously referred to in connection with the holding circuit for relay 201 and group relay 314. When relay 401 is energized. relay 402 also operates over a circuit extending from grounded battery, winding of relay 402, brush 403 in its normal position, conductor 404 to ground at the left armature of relay 401. If the de sired number is within the groups of lines (Z' or (Z of the final selector switch D, shown in Fig. 3, the impulse sending device at substation A is operated to transmit either one or nine impulses, depending in which group the line selecting operation is to take place. Assuming that the called number is in group cl, the sending device is operated to transmitone impulse, and 1n response thereto the armature of relay 400 will be retracted and close a circuit for the stepping magnet 405 extending from grounded battery, winding of magnet 405, front contact and mner left armature of relay 402,

winding of slow-to-release relay 406, back' contact and left armature of relay 407, right armature of slow-to-release relay 401 and back contact and armature of relay 400 to 7 ground. The brushes of the switch are thereby stepped onto the second set of tersaid relay 408 locked up through its outer most lower armature and front contact. armature and back contact of relay 409 and left armature of slow-to-release relay 401. to ground. The group of trunks d has now been selected and at the termination of the impulse, slow-to-release relay 406 deener izes, but relay 402 remains energized over a circuit extending from grounded battery, winding of relay 402, brush 403, conductor 404 and left armature of slow-to-release relay 401 to ground. Upon transmitting the units impulses to select the desired line in the group cl, stepping magnet 405 is again operated over the previously de scribed circuit to step the brushes of the switch. It is to be noted that as soon as the brush 403 leaves the second terminal, ground will no longer be found for relay 402 at the left armature of slow-to-release relay 401, but relay 402 will remain energized over a circuit extending from grounded battery, winding of said relay, left armature and back contact of group relay 410 and left armature of slow-to-release relay 406 to ground. Relay 406 remains energized during the transmission of impulses. Stepping magnet 405 will thus continue to operate in accordance with the impulses transmitted until the brushes have been stepped upon the desired set of terminals. If the line selected is found to be busy, relay 402 will continue to find ground at the left armature of slow-to-release relay 406 until the same becomes deenergized at the termination of the impulses, whereupon the circuit for relay 402 will be extended from the back contact of the left armature of relay 406. through relay 407, inner right armature and back contact thereof, front contact and outer left armature of relay 402, brush 411 to ground at the busy terminal of the called line. Relay407 will lock up through its inner right armature to ground at the left armature of relay 401. Attraction of the outer right armature of relay 407 furnishes a busy tone to the calling line extending from grounded battery, right winding of line relay 400, lower side 01 the subscribers line, substation apparatus A, upper side of subscribers line, outer right armature of relay 407 and coil BZ to ground.

Shouldthe called line be idle, relay 402 releases at the end of the impulses, since upon denergization of relay 406 the ground at the left armature of the latter relay will be removed. Upon the release of relay 402, relay 412 becomes energized over a circuit extending from. grounded battery, winding of relay 412, right armature and back contact of relay 402, back contact and innermost right armature of group relay 410, brush 413 and back contact and right armature of slow-to-release relay 406 to ground. Energization of relay 412 extends the line to the selected terminals and closes a circuit for relay 409 extending from the ringing current generator 414, right Winding ofrelay 409, front contact and inner lower armature of relay 408, lower armature and front contact of relay 412, ringer apparatus at the called substation E, front contact and upper armature of relay 412 and inner upper armature of relay 408 to ground. Ringing current is thus applied to the line and is also induced into the secondary winding of relay 409 for the purpose of furnishing ringing tone to the calling station, the circuit for this ringing tone extending from grounded battery, left winding of relay 415, lower side of the telephone line, substation apparatus A, upper side of the telephone line, right winding of relay 415 and left winding of relay 409 to ground. Relay 409 is marginal and will not, attract its armature as long as the resistance of the substation bell is in its circuit, but when the receiver at the called substation E is remo said relay will become energized and break the circuit for relay 408 which extended through the armature and back contact of said relay 409. Relay 408, in releasing, disconnects the ringing current and closes the talking circuit at the innermost upper and lower armatures and back contacts, and conversation may proceed.

If the called line had been located in group d it would have been necessary to transmit nine impulses to the final selector to step the brushes thereof onto the tenth terminal shown in the bank of the selector D in Fig. 3, and in so stepping the brushes the operation would be precisely the same as that set forth above. It should be noted that no line numbered 91 appears, since the terminal which. should have been allotted for line 91 is, instead, allotted for the selection of group (Z Should the line be in group 03 the brushes are stepped around as previously described until they engage the eleventh terminal shown in Fig. 3, whereupon as soon as relay 406 releases at the end of the impulses, group relay 410 is energized by a circuit ex tending from rounded battery, Winding of relay 410, conductor 416, brush 413, back contact and armature of relay 406 to ground.

he operation of relay 410 energizes relay 402 over the circuit extending from grounded battery, winding of relay 402, left armature and front contact of relay 410 to ground. Ene'rgization of relay 410 also closes. a circuit for stepping magnet 405 extending from grounded battery, winding of magnet 405, armature and back contact thereof, outermost right armature and front contact of relay 410, conductor 416, brush 413, back contact and armature of relay 406 to ground. Magnet 405 is now self-interrupting and operates to automatically step the brushes of the switch. Upon the first step of said brushes, relay 410 looks up over the circuit extending from grounded battery, winding of relay 410, front contact and innermost right armature thereof, conductor 417, brush 413, back contact and armature of relay 406 to ground. The stepping operation "of the brushes continues until brush 413 reaches the terminal having no connection to the conductor 417, whereupon said brushes come to rest on this set of terminals. Relay 410 releases, but relay 402 continues to be energized over a circuit from grounded battery, winding of relay 402, brush 403, conductor 404 and left armature of islow-to-release relay 401 to ground. In response to the units impulses, the brushes are again stepped around in the line selecting movement in group 05 'n the same manner as previously described for calling a number in group 0?.

Should the subscriber after initiating a call, hang up his receiver before an idle trunk leading to the'selector switch has been seized, it will be apparent that the line switch will continue to hunt for the idle trunk, and upon finding the same, cutoff relay 201 will be energized as previously described. Relay 307, being in series with relay 201, also energizes, and at its front contact, closes a circuit for line relay 309, which in attracting its armature, energizes slowto-release relay 305, thus grounding conductor 304 leading from cutoff relay 201, at the left armature of relay 305, instead of at the back contact and right armature of relay 301 and thereby shunting relay 307. Re-' l ase of this relay deenergizes line relay 309, since the line circuit has been broken by replacing the receiver, and armature of relay 309 closes the circuit of stepping mag.- net 313 extending over the previously traced circuit, and the brushes are stepped onto the second set of terminals. In response to. the continued deenergization of relay 309, relay 305 releases, and after an interval relay 301 follows. Group relay 320 is then energized over a circuit extending from grounded battery, winding of relay 320, brush 308, back contact and inner right armature of test relay 303, back contact and right armature of slow-to-release relay 301 to ground. The right armature of group relay 320 puts ground on the set of test terminals associated therewith, and test relay 303 is consequently energized by the circuit extending from grounded battery, right winding of relay 303, brush 316, front contact and right armature of relay 320 to ground. Energization of relay 303 closes the circuit'for stepping magnet 313 from grounded battery, winding of magnet 313, armature and back contact thereof, front contact and outer left armature of relay 303, back contact and left armature of slow-torelease relay 305 to ground, the latter relay having become deenergized upon the release of line relay 309. The brushes are now stepped to the next set of terminals, and this action takes place each time the brush 316 engages one of the terminals which finds ground at the right armature of group relay 320. When engaging the test terminals of the different groups 0, c and 0 brush 316 finds ground for test relay 303 at the back contacts and armatures of the respective group relays. When relay 320 is energized, ground for the group of terminals 0 extends from the armature and back contact of relay 309, outer lower armature and back contact of relay 310, right armature and back contact of relay 305, outermost and middle left armatures and front contacts of relay 320 to said terminals. Stepping magnet 313 continues to operate until the last set of terminals is reached. whereupon the switch is stepped to normal as previously described. It is to be understood that the terminals indicated by dot ted lines over which brush 316 moves, are connected to the other terminals of the re spective groups in the same manner as shown in full lines. Upon the shunting of relay 307, relays 309 and 305 will release and the holding circuit for relay 201 will be broken at the left armature of relay 305. Stepping magnet 202 will then operate to step the switch B to normal over the circuit extending from grounded battery, winding of magnet 202, armature and back contact thereof, lowermost armature and back contact of relay 201 and brush 205 to ground at the armature and back contact of line relay 200.

At the termination of a conversation, in the event that a connection has been established between the calling and called substations, the hanging up of the receiver at substation A releases line relay 400 of the final selector switch D, which also causes slow-to-release relay 401 to deenergize. Relay 410 now energizes over the circuit extending from grounded battery, winding of relay 410, brush 418, back contact and right armature of slow-to-release relay 401, back contact and armature of relay 400 to ground. Energization of relay 410 breaks, at its innermost right armature and back contact, the circuit for relay 412, causing this relay to release. Stepping magnet 405 is now operated over the circuit extending from grounded battery, winding of magnet 405, armature and back contact thereof, outermost right armature and front contact of relay 410, brush 418, back contact and right armature of slow-to-release relay 401, back contact and armature of relay 400 to ground, and stepping magnet 405 continues to operate until the switch is stepped to its normal position where the circuits for'said re lay 410 are broken.

In order to prevent the selector switch D from being seized during the return of the switch to its normal position, it being understood that the busy ground has been removed by the deenergization of slow-to-release relay 401, a ground is providedat the middle right armature and front contact of relay 410.

The removal of ground at relay 401 releases group relay 314 of selector switch C, and places ground on all trunks of the selected group associated with said relay, and thereby energizes test relay 303 over a circuit extending from grounded battery,'right winding of relay 303, brush 316, terminal of the selected trunk,back contact and right armature of relay 314 to ground. Test relay 303, pulling up, opens at its right armature and back contact, the circuit for cutoff relay 310 and closes the circuit for stepping magnet 313 extending from grounded battery, winding of magnet 313, armature'and back Mtact thereof, front contact and outer left armature of relay 303, back contact and left armature of relay 305 to ground, and stepping magnet 313 continues to operate as long as brush 316 engages a terminal which finds ground at the right armature of relay 314, and will also operate upon each en gagement of brush 316 with the test terminals associated with group relays 315, 320 and 321 which are deenergized. If the brushes have selected an idle trunk in groups 0 nal to which they would be stepped when selecting group of trunks c relay 303, in passing over said terminal, will be energized by the circuit extending from grounded battery, right winding of relay 303, brush 316,

conductor 322, back contact and left arrna ture of relay 305 to ground, and stepping magnet 313 will thus again step the brushes onto the next set of terminals.

Line switch B is also returned to normal by the removal of ground at left armature of slow-to-release relay 401 which causes the release of cutoff relay 201, this relay and 0 before reaching the termi having been held energized by the circuit extending from grounded battery, winding of stepping magnet 202, armature and back contact thereof, winding of relay 201, brush 204, conductor 304:, left armature and back contact of relay 301, back contact and inner left armature of relay 303, brush 317 and left armature of relay 401 to ground. The release of relay 201 energizes stepping magnet 202 over a circuit extending from grounded battery, winding of magnet 202, armature and back contact thereof, lowermost armature and back contact of relay 201 and brush 205 to ground at the armature and back contact of line relay 200. Stepping magnet 202 continues to operate until the brushes thereof engage the normal terminals, whereupon the operating circuit of said magnet will be broken and the switch will come to rest.

If it is desired to establish a connection to a central oflice, subscriber at Substation A, by removing his receiver, will operate line switch B to select an idle trunk leading to one of the first selectors, and upon transmitting a single impulse the brushes of said selector will be stepped, as previously described, onto the second set of terminals, and thus select the group of trunks c for the trunk hunting operation which automatically takes place in the same manner as described in connection with the extension of a call through group of trunks 0', group relay 320, in this instance, becoming energized. V

Should the service of substation A be restricted, a conductor 207 is employed to connect the middle lower armature of cutoff relay 201 of the line switch with brush 206 so that if an attempt is made to call the central ofiice from this station, energizetion of cutoff relay 201 will apply said ground to the central ofiice trunks and cause the same to test busy, said ground extend ing through conductor 207, brush 206, conductor 323, front contact and middle left armature of group relay 320, which has become energized, to the terminals of the central office trunks. Stepping magnet 313 will therefore continue to operate until the last set of terminals is reached, whereupon test relay 303 will be energized over a circuit extending from grounded battery, right winding of relay 303, brush 316, the last test terminal, outermost left armature and front contact of relay 320, conductor 323, brush 206 and middle lower armature and front contact of relay 201 to ground, thus causing the stepping magnet'to again operate and return the switch to normal position. Line switch B, however, remains in its actuated position aslong as the receiver is off the switchhook, and the subscriber may again manipulate his dial to call the private branch exchange operator.

To establish a connection to the private branch exchange operators position, the sending device at substation A is actuated after the seizure of an idle trunk bythe line switch B, to transmit ten impulses to step the brushes onto the eleventh set of terminals, whereupon group of trunks 0 will be selected for the trunk hunting operation, and in this case group relay 321 will be energized, to remove ground from the terminals of the private branch exchange trunks over which test brush 316 passes and one of the trunks will be seized in the same manner as previously described.

What is claimed is:

1. In a telephone exchange system, a selector switch having a terminal bank, groups oftrunks connected to certain terminals of said bank, other terminals thereof being allotted for group selection, and means for moving the switch over the last named terminals and terminals of groups of trunks in selecting an idle trunk in a selected group.

2. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank and having their terminals interspersed, other terminals of said bank being allotted for group selection, and means for moving the switch over terminals allotted for group selection and also terminals of non-selected groups in selecting an idle trunk in a selected group.

3. In a telephone exchange system, a ro tary selector switch having a terminal bank, groups of trunks connected to said bank and having their terminals arranged in interspersed relation, other terminals of said bank being allotted for the selection of a particular group, and means for moving the switch over terminals allotted for group selection and also terminals of a nonselected group in selecting an idle trunk-in a selected group.

a. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank, other terminals of said bank being allotted for group selection, one of said other terminals being arranged between terminals of two of said groups, and means for moving the switch over said other terminals and also terminals of certain groups in selecting an idle trunk in another group.

5. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to said bank and having their terminals interspersed, other ter- 6. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to said bank and having their terminals interspersed, other groups of trunks also connected to said bank, certain other terminals of said bank being allotted for group selection, one of the latter terminals being arranged between terminals of the first named groups, and means for moving the switch over said other terminals, and terminals 01 said first named groups in selecting an idle trunk in one of the second named groups. 7

7. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to said bank and having their terminals interspersed, other groups of trunks also connected to said bank, cer tain other; terminals of said bank being allotted for group selection, one of the latter terminals being arranged between terminals of the first named groups, and means for moving the switch over the other of said latter terminals and terminals of the first named groups and onto the terminal arranged between terminals of said first named groups to select one of the second named groups for trunk hunting operation therein.

8. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank, test terminals for said groups,

a relay assigned to each group, means for energizing one of said relays to place a certain electrical condition upon the test terminals of the group of trunks associated therewith, and means for moving said switch over other test terminals of said group until a terminal is found havingthe same electrical condition as the first named test terminals of said group.

9. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank, test terminals for said groups,

electromagnetic means assigned to each' group, means for energizing one of said electromagnetic means to place a certain electrical condition upon terminals of the group of trunks associated therewith, and means for moving said switch over other test terminals of said group until a terminal is found having the same electrical condition as the first named test terminals of said group.

10. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank having their terminals interspersed, test terminals for said groups, electromagnetic means assigned to each group, means for energizing one of said electromagnetic means to place a certain. electrical condition upon terminals of the group of trunks associated therewith, and means for moving said switch over other test terminals said group until a terminal is found having the same electrical condition as the first named test terminals of said group.

11. In a telephone exchange system, a se' lector switch having a terminal bank, groups of trunks connected to certain terminals of said bank, other terminals being allotted for group selection, test terminals for said groups, means for selecting one of said other terminals, means operated thereupon to place a certain electrical condition upon test terminals of the selected group, and means for moving the switch over certain of said other terminals and terminals of the selected group in selecting an idle trunk therein.

12. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank, other terminals being allotted for group selection, test terminals for said groups, means for selecting one of said other terminals, means operated thereupon to place a certain electrical condition upon test terminals of the selected group, and means for moving the switch to hunt an idle trunk in the selected group, the test for said idle trunk being predetermined by the finding of another test terminal having the same electrical condition as the test terminals of the selected group. I

13. In a telephone exchange system, aselector switch having a terminal bank groups f trunks connected to certain terminals of said bank, test terminals for said groups, a relay assigned to each group, means for energizing one of said relays to place a certain electrical condition upon the test ter- 7 minals of the group of trunks associated therewith, and means for moving said switch over other test terminals of said group until a terminal is found having the same electrical condition asthe first named test terminals of said group, the last named means being operated by the finding of a certain other electrical condition at an armature of said relay. 7 7

Q 14. in a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank and having their terminals interspersed, other terminals ofsaid bank being allotted for group selection, test terminals for, said groups, means for selecting one of 7 lector switch having a terminal bank, groups of trunks connected to certain terminals of said bank and having their terminals interspersed, other terminals of said bank being allotted for group selection, test terminals for said groups, means for selecting one of said other terminals, means operated thereupon to place a certain electrical condition upon test terminals of the selected group, and means for moving the switch to hunt an idle trunk in the selected group,

the test for'said idle trunk being determined by the finding of another test terminal having the same electrical condition as the test terminals of the selected group.

16. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to certain terminals of said bank and having their terminals interspersed, test terminals for said groups, a relay assigned to each group, means for energizing one of said relays to place a certain electrical condition upon the terminals of the groups of trunks appropriated therewith, and means for moving said switch over other test terminals of said group until a terminal is found having the same electrical condition as the first named test terminals of the gr0up,-the last named means being operated by the finding of a certain other electricalcondition at an armature of said relay. 7 V

17. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to said bank and having their terminals interspersed, other terminals of said bank being allotted for group selection, a line relay, a stepping magnet responsive to interruptionslat said line relay for moving the switch onto one of said other terminals to select the associated group of trunks, a relay assigned to each group, means for energizing the-last named relay I when the associated group is selected, and a circuit for said stepping magnet closed upon energization of said last named-relay for causing saidstepping magnet to'move the switch over terminalsof the selected group to hunt an idle trunk therein.

18. In a telephone exchange system, a selector switch having a terminal bank, groups of trunks connected to said bank, other terminals of said bank being allotted for group selection, a line relay, electromagnetic means responsive to interruptions at said line relay for moving the switch onto one of said other terminals to select the associated group of trunks, other electromagnetic means assigned to each group of trunks, means for energizing said other electromagnetic means when the associated group is selected, and a circuit for the first named electromagnetic means closed. upon energization of said other electromagnetic means for causing said first named electromagnetic means to move the switch over terminals of the selected group to hunt an idle trunk therein.

19. In a telephone exchange system, a telephone line, a selector switch for extending said line and having test brushes, groups of trunks served by said switch, means for operating said switch to select a group of trunks, electromagnetic means associated with each group of trunks and energized upon the selection thereofto place a certain electrical condition upon the terminals of said group, and means for operating the switch to hunt an idle trunk in the selected group, the seizure of a trunk depending upon the test brushes simultaneously engaging terminals having said certain electrical condition.

20. In a telephone exchange system, a telephone line, a rotary selector switch for extending said line and having test brushes, groups of trunks served by said switch and having their terminals interspersed, a stepping magnet operable to step said switch to select a group of trunks, a relay associated with each group of trunks and energized upon the selection thereof to place a certain electrical condition upon the terminals of the selected group with which one of said test brushes is associated, and means for con-' tinuing the operation of said stepping magnet until the other test brush engages anassociated terminal having the same electrical condition as that applied to the last named terminal.

21. In a telephone exchange system, a.

telephone line,a' selector switch for extending said line, a terminal bank for said switch, groups of trunks connected to cer-. tain of the terminals of said bank, other terminals being allotted for group selection, means for stepping said switch over certain of said other terminals to select one of them, and means for continuing the operation of said stepping means whereby the brushes of the switch are caused to move over terminals of non-selected groups in seeking an idle trunk in the selected group.

22. In a telephone exchange system, a telephone line, a selector switch for extending said line, a terminal bank for said switch, groups of trunks connected to certain of the terminals of said bank, other terminals being allotted for group selection, means for stepnecting the calling line to the called line and including a terminal bank, groups of trunks connected to certain of the terminals in said bank, other terminals being allotted .for 'group selection, and directively controlled means moved over certain of said other terminals and also terminals of certain groups in selecting an idle trunk in the selected group leading to said called substation line.

24. In a telephone exchange system, calling and called substation lines, an impulse sending device at the calling substation, switching means for extending a call from the calling substation line, selector switch for connecting the calling line to the called line and including a terminal bank, groups of subsfribers lines connected to certain of the terminals in said bank, other terminals being allotted for group selection, directively controlled means moved over certain of said other terminals in response to the tens impulses of the called number to select one of said groups and moved over the terminals of the selected group in response to the units impulses of said called number to seize the called line, and means for automatically operating said directively controlled means during the interval between the transmission of the tens and units impulses to move said means over terminals of a non-selected group.

25. In a telephone system, a trunking ar-- rangement comprising groups of trunks, the trunks of one group being promiscuously interspersed between the trunks of other groups, means to select a group, and means to select a trunk in said selected group.

26. In a telephone system, a trunking arrangement comprising groups of trunks, the trunks of one group being promiscuously interspersed between the trunks of other groups, and means to simultaneously identify a group and an idle trunk in that group.

27. In a telephone exchange system, a selector switch having fixed terminals and moving contacts cooperating therewith, groups of lines connected to said terminals, other terminals being alloted for group selection, lines of said groups and said group selection terminals being interspersed in order of their appearance, and means for moving said contacts over said terminals to select an idle line.

28. In a telephone exchange system, a

selector switch having a terminal bank, groups of subscribers lines connected to certain terminals of said bank, other terminals being allotted 'for group selection, direc-- tively controlled means for moving the switch over terminals of one of saidgroups,

and means for automatically moving the switch over terminals of another group to select still another group for a line selecting operation therein. 7 29. In a telephone exchange system, a se lector switch having a terminal bank, groups of subscribers lines connected to certain terminals of said bank, other terminals being allotted for group selection, directively con-.

of subscribers lines connected to certain terminals of said bank, other terminals being allotted for group selection, directively controlled means for selecting one of said other terminals, and means for automatically moving the switch over certain line terminals in selecting the group of subscribers lines associated with said other terminal. v

'31. In a telephone exchange system, a single movement switch, groups of subscribers lines terminating in said switch, means for selecting a group decimally and automatically, and means for then selecting a line decimally. p

32. In a telephone'system, a switch having a movement in a single plane, a wiper for said switch, groups of subscribers lines terminating in said switch,'said subscribers lines being decimally designated, and means responsive to trains of impulses to step said wiper to select a group of lines and a line in said group, the steps of said wiper in the group and line selecting movements being of equal length.

83. In a telephone exchange system, an impulse sending device, a switch responsive to said sending device and comprising stationary terminals, and a movable terminal arranged to move in a single plane, a plurality of groups of subscribers lines terminating in said stationary terminals, and means responsive to impulses sent by said sending device on a decimal basis for moving said movable wiper to select a group and a line in said group, the movements of the wiper being of equal length.

34. In a telephone exchange system, an automatic switch, a terminal bank therefor, groups of lines connected to certain terminals on said bank, other terminals being allotted for group selection and interspersed between said groups of lines, means for selecting a group of lines decimally, and means for selecting a line decimally.

35. Ina telephone exchange system, a switch having a movement in one direction only, groups of connectors, groups of trunks connected'to said switch and terminating in said connectors, other groups of trunks, op-

groups of trunks connected to said switch and terminatingv at said positions, and

means operated by a single set of impulses for moving said switch to select any one of said trunks.

37. In a telephone exchange system, a switch having a movement in one direction only, a plurality of trunks connected to said switch for extending a calling line toward a called line, a plurality of other trunks for extending a calling line to an operators position, a stepping magnet for moving said switch to select any one of said trunks, and means whereby said stepping magnet will restore said switch to normal.

38. In a telephone exchange system, a switch having a movement in one direction only, a plurality of trunks connected to said switch for extending a calling line toward a called-line, a plurality of other trunks for extending a. calling line to an operators position, a stepping magnet operated by a single set of impulses for moving said switch to select any one of said trunks, and

means whereby said stepping magnet will restore said switch to normal.

39; In a telephone system, a trunking arrangement comprising groups of trunks, the trunks of one group being promiscuously interspersed between the trunks of other groups, and means to identify a group and an idle trunk in that group.

f In witness whereof we hereunto subscribe pur names this 23rd day of December, A. D.,

SAMUEL B. WILLIAMS, JR. BER-T e. DUNHAM. 

